3. Role of Quorum Sensing in Fungal Morphogenesis and Pathogenesis

Abstract

Fungi are simple organisms yet complex in their morphology. They have evolved in several ways to cope with diverse environmental conditions which they encounter. Some produce dormant structures which help them to survive unfavorable conditions, while others, especially pathogens, have adopted dimorphic form to adapt to new conditions. In many pathogenic fungi, the hyphae are responsible for penetration either through natural openings or via invasion of tissue. Once inside the host, morphogenesis, which is many a times under quorum-sensing regulation, is triggered that enables the mycelium to switch to yeast phase that can now spread in the host with higher efficiency as well as evade host immune responses. Although very few fungi are known to regulate both morphogenesis and pathogenesis via quorum sensing (QS), it is believed that quorum-sensing regulation of at least morphogenesis is a universal phenomenon across all fungi. However, a systematic evidence for this is lacking. A wide array of inducer molecules, such as Butyrolactone I, phenylethanol, tyrosol, farnesol, oxylipin, and farnesoic acid among many others, have been identified in fungi till date. In addition to these chemical compounds, a calcium-binding protein (CBP) is also involved in quorum-sensing regulation of morphogenesis and pathogenesis in the genus Histoplasma. Quorum sensing has well-established applications in controlling the spread of diseases as an alternative strategy to the use of antibiotics and overcoming multidrug-resistant strains. While there are numerous potential inhibitors of quorum-sensing inducers, not even a single effective molecule, which is also economically viable, has been commercialized till date. The research in this field therefore demands a more systematic and coordinated effort to investigate quorum sensing and quenching molecules across the diverse taxa within fungi.